This invention relates to a cable length adjustment device, and more particularly to a device suitable for length adjustments of cables in any system requiring precise adjustment, such as those found in park interlock cable systems of automobiles.
In a park interlock system of an automobile, a cable is utilized to connect a translatable gearshift mechanism to an ignition key tumbler in such a fashion so as to prevent the automobile from shifting out of "park" without an ignition key in the tumbler or to prevent the removal of the ignition key without the gearshift mechanism being in "park". Due to the precise settings required in such systems, the correct cable length is essential to the proper operation of such systems.
To ensure that the cable is a proper operating length, cable length adjusters are utilized to perform fine adjustment. The cable length adjusters generally include a cable having a conduit or sheath with a longitudinally extending bore for movably receiving a cable core. An elongated member is attached at one end to the conduit of the cable and at the other end to the gearshift mechanism. A locking member is provided which is mounted on the elongated member in a manner which, when unlocked, allows for sliding movement between the elongated member and the locking member and when locked, prevents movement of the elongated member with respect to the locking member. Adjustment means are provided which allow the locking member to engage the elongated member in predetermined increments along the elongated member thereby adjusting the length of the conduit to achieve the appropriate cable length. Examples of such adjusters include U.S. Pat. Nos. 4,418,583, 3,710,645 and 3,572,159.
The conduit adjust type mechanisms described above suffer from a number of shortcomings. The most significant is the need for there to be sufficient slack in the conduit to allow the elongated member to slide freely within the adjuster. In many cases, the conduit is routed underneath carpet or is fixed in place by a location clip to avoid interference with mating components. In these instances, the conduit cannot move freely and the adjustment is biased or unattainable.
Furthermore, the locking members of the prior devices in general, have closed internal diameters. Hence, material must be added to their external circumferences to create raised surfaces for locking features to act against. In addition to not efficiently maximizing valuable space, this design requires that the threaded area of the locking member be created in a secondary tapping operation and since a thread lead cannot be achieved by conventional tapping operations, they are not possible with the closed diameter type devices. Another disadvantage of the closed internal diameter type device is that the threaded area of the locking member rides against the elongated member biasing adjustment due to partial engagement of the threads.
Additionally, the above-described cable length adjusters generally do not provide a fine adjustment means required for many purposes. Specifically, access to the locking member is limited because of the design of the adjuster, and the adjustment increments are typically too large to accommodate cable length discrepancies such as those found in park interlock systems. Further, the adjusters are constructed of a plastic material which does not meet new automobile engine design requirements of temperature and strength.
Finally, none of the prior art devices disclose a visual means whereby a user of the device can identify the locked position of the mechanism. While many of the devices provide an audible "snap" when the device is locked, this may be ineffective, particularly in a noisy factory or repair shop.